It *might* be possible, but it would definitely probably require some hacking of the core code. The mixing of flat and threaded in different areas isn't possible out of the box.
You'd also need to heavily modify the templates to maintain that same look.
Anything is possible if you're comfortable with php, but it really depends on how much you want to modify the code. It's pretty safe to say with the amount of modification you'd need to do it would be pretty tough if you wanted to upgrade to new versions as they came out.
